Subterranean termites most often enter structures from the surrounding soil to feed on wood, or other cellulosic material, of the structure and its contents. If unchecked, termites can cause considerable damage. As a result, efforts to erect physical or chemical barriers to prevent the entrance of termites into a structure or to exterminate the termites after they have invaded a structure have proven a considerable expense to the public (Su, N. Y., J. H. Scheffrahn [1990] Sociobiol. 17(1):77-94). The cost to control termites in the United States exceeds one billion dollars annually (Mauldin, J. K, S. C. Jones, R. H. Beal [1987] The International Research Group on Wood Preservation Document No. IRG/WP/1323).
Subterranean termites construct an extensive foraging gallery beneath the soil surface. A single colony may contain several million termites with foraging territory extending up to 300 feet (Su, N. Y., R. H. Scheffrahn [1988] Sociobiol 14(2):353-359). Since subterranean termites are a cryptic creature, their presence is not normally known until after some damage, foraging tubes, or live termites such as swarmers, are found. Some subterranean termites are known to forage beneath an object on the soil surface (Ettershank, G., J. A. Ettershank, W. G. Whitford [1980] Environ. Entomol 9:645-648).
Currently, there are two basic approaches for the control of subterranean termites: preventive control and remedial control. In some of the United States, it is mandatory that the soil underlying the foundation of newly constructed buildings be pre-treated with a pesticide (also referred to herein as termiticide) to prevent termite infestation. Pesticide is typically sprayed over and into the soil prior to construction. This pre-construction treatment produces a horizontal barrier beneath the building. Because of the lack of communication between pesticide applicator and construction workers, the barrier often loses its continuity during the construction. Moreover, the currently available soil termiticides tend to lose their biological activity after five or more years to the extent that the treated soil is no longer effective against termite invasion. Established termite colonies in the soil may then invade the structure if additional chemical is not applied beneath and around the structure.
When a house or other building is infested by subterranean termites, efforts are made to create a continuous barrier beneath the building in the soil where the subterranean termites are provided access to the building. A common method of creating this barrier is to introduce termiticide around a building foundation by injection into soil underlying concrete foundations, drenching the soil surrounding the building perimeter, or a combination of both. This type of post-construction treatment is labor-intensive and may not adequately produce a continuous barrier (Frishman, A. M., B. L. Bret [1991] Pest Control 59(8):48, 52, 54, 56; Frishman, A. M., A. St. Cyr [1988] Pest Control Technology 16(4):33, 34, 36).
Other remedial treatments include spot treatments such as dusting or injecting termiticides within the walls of the building. Robert Verkerk has described arsenic trioxide dust treatment using termite lures (Verkerk, R. [1990] Building Out Termites, Pluto Press Australia Limited, P.O. Box 199, Leichhardt, NSW 2040). Verkerk describes the use of stakes or blocks of termite susceptible timber to lure termites after the stakes or blocks have been placed near a known termite problem. Once termite activity is observed, arsenic trioxide is injected. Alternatively, a portion of the termites may be dusted with arsenic trioxide.
Most spot treatments are done to stop existing termite infestations at a particular area in a structure but generally affect only a small portion of the subterranean termite population, i.e., those termites which come into direct contact with the pesticides. Because of the extensive foraging populations and expansive territory of subterranean termite colonies, the vast majority of the termite population is not affected by such spot treatments.
U.S. Pat. No. 3,940,875 describes a method, however impractical, for dispensing termite poison in the soil in an attempt to extend the life of the barrier type treatment such that the presence of termites is signalled by the release of an odor when the termites feed on the poison. The '875 patent also describes a termite-edible container which gives off an odor when eaten by a termite. In addition to the '875 patent and the Verkerk article referenced above, other publications describe the use of termite-edible materials as components of schemes to control termites. For example, Japanese patent application Nos. 61-198392 and 63-151033 describe wooden vessels specifically designed to “attract” termites as part of a monitoring procedure. The 61-198382 application describes a vessel preferably made from pine or cedar, used in an attempt to attract termites. The 63-151033 application also uses a wood attractant to entice termites. In the 63-151033 application, the termites are further exposed to a toxicant which is then presumably carried back to the nest in hopes of killing the queen via trophallaxis or food exchange. Neither Japanese application provides any data establishing that the described process actually has any impact on termite populations. Furthermore, there is no indication that it is possible to “attract” termites at all. These methods have further important disadvantages. For example, the wooden inducing body will be subjected to fungal decay before termite attack, especially in moistened soil Thus, frequent replacement of the inducing body is needed during the monitoring period. Further, damage to the inducing body can result in the penetration of the termiticide into the ground. This is not environmentally acceptable.
One termite control method comprises placing a highly toxic material, such as an arsenic-containing dust, at a site of infestation in the hope that this will directly control an effective number of termites at the site and also other termites back in the colony. However, this method relies on pumping toxic dust into a termite tunnel and depositing relatively large quantities of dust.
Elaborate schemes of pipes to convey liquid termiticides under and surrounding buildings have also been proposed for termite control. It has been suggested that these liquid termiticides may be dispensed into the soil surrounding and below the building through these pipes to provide a continuous barrier to the incursion of termites. This method requires a large quantity of termiticides in order to saturate the soil surrounding the building.
U.S. Pat. No. 5,027,546 describes a system intended for use on above ground termites, i.e., drywood termites, which controls termites by freezing with liquid nitrogen. Although the liquid nitrogen is essentially non-toxic in that no toxic residues persist, it is hazardous to use and the method is a spot treatment and will not affect the majority of termites. U.S. Pat. No. 4,043,073 describes a method which attempts to circumvent the problem of repeated application of pesticide. The described method functions by “encapsulating” the insecticide, thus making it more persistent. The overt use of pesticides and their persistence in the environment are not remedied by this system. Another proposed system which fails to alleviate the problem of transferring insecticide directly into the soil is U.S. Pat. No. 3,624,953. This method employs a reservoir of insecticide wherein the vapors of the insecticide are permitted to permeate the soil surrounding the reservoir. Thus, exposure of the environment with toxic substances is not avoided by using this method.
Toxicants which have less environmental effect and which show activity against termites are known (Su, N.Y., M. Tamashiro, M. Haverty [1987] J. Econ. Entomol. 80:1-4; Su, N.Y., R. H. Scheffrahn [1988] Florida Entomologist 71(1):73-78; Su, N. Y., R. H. Scheffrahn [1989] J. Econ. Entomol. 82(4):1125-1129; Su, N.Y., R. H. Scheffrahn [1990] Sociobiol. 17(2):313-328; Su, N.Y. [1991] Sociobiol. 19(1):211-220; Su, N.Y., R. H. Scheffrahn [1991] J. Econ. Entomol. 84(1):170-175; Jones, S. [1984] J. Econ. Entomol. 77:1086-1091; Paton, R., L. R. Miller [1980] “Control of Mastotermes darwiniensis Froggatt (Isoptera: Mastotermitidae) with Mirex Baits,” Australian Forest Research 10:249-258; McHenry, W. E., U.S. Pat. No. 4,626,528; Henrick, C. A., U.S. Pat. No. 5,151,443). However, none of these toxicants have previously been used in conjunction with a method which efficiently and efficaciously delivers the toxicant to a target pest.
Australian Patent No. 1,597,293 (the '293 patent) and a corresponding Great Britain Patent, No. 1,561,901, describe a method which involves mixing insecticide with a food matrix comprising cellulose and a binding agent. The method described in the '293 patent relies on the termite ingesting the insecticide along with the matrix, then returning to the colony to introduce the insecticide to other termites through the natural process of trophallaxis (food exchange between termites). However, the '293 patent describes usages only when termites are known to be present and, furthermore, the described method fails to ensure that the termites will initially find the matrix and relies on those termites finding the matrix to transfer sufficient amounts of the insecticide to the colony solely by trophallaxis. Like the Japanese patent application No. 63-151033, the method of the '293 patent requires that the matrix is more attractive to the termites than surrounding materials. The method described in the '293 patent relies on the moisture in the matrix (supposedly retained by the binding agent, agar) to attract termites. The described method, therefore, is primarily for termite species that are attracted to moisture (or those under “water stress”). Moreover, the '293 method fails to assure that the moisture will remain in the baits when applied in the field awaiting termite arrival. This is an unrealistic requirement for a practical application, because even a moistened sawdust-agar matrix will desiccate within a few days when placed in a dry soil.
It should be noted that attractants other than water for termites have been investigated. For example, the extract from brown-rot fungi chemically resembles the trail-following pheromones of termites. Natural pheromones, however, are species-and even colony-specific. A pheromone that is “attractive” to one species or colony of termites may repel termites of other species or colonies. It is of uncertain value, therefore, to incorporate pheromone mimics (such as the brown-rot fungi extract) in a bait, especially if a bait is to be used against a wide range of termite species.
It should also be noted that trophallaxis is an uncertain means of delivering the insecticide to the colony because it assumes that digestive enzymes and other metabolic processes do not affect the active ingredient. However, once the insecticide is ingested by the termite, the insecticide may be rendered inactive by the digestive process of the termites. Moreover, suppression of a termite population requires that a substantial number of termites in the colony are disabled before their damage potential is diminished Relying only on trophallaxis to transfer the toxicant does not ensure that adequate numbers of termites will be controlled.
Modifications to the method described in the '293 patent may not increase the bait intake of termites. For example, the '293 method requires that the matrix mixture be applied at a known infestation site such as a termite mound or tree trunk. This method, therefore, can be used only as a remedial treatment. The '293 method cannot be used unless activity of termites is detected. The '293 patent also proposes that a large quantity of toxicant bait be placed at random locations as a preventative measure. However, without providing a procedure for detecting termites, the majority of this bait may desiccate or degrade due to fungal growth and become unpalatable to termites. Moreover, an unnecessarily large quantity of toxicant is applied in the environment.
It is therefore highly desirable to more effectively control termites or other insects in a manner which assures that the termites or other insects of interest are exposed to the toxicant, which minimizes environmental harm by reducing the amount of insecticide used, and which affects adequate numbers of termites in a colony.